The main goal of this thesis was to develop new methods and knowledge that will explain and predict species differences in sensitivity to dioxin-like compounds (DLCs) in birds. The important achievements and results obtained from the four experimental chapters of this thesis are summarized as follow: (1) an efficient luciferase reporter gene (LRG) assay was developed for use with 96-well cell culture plates; (2) the results obtained from LRG assay were shown to be highly correlated to available in ovo toxicity data; (3) amino acids at positions 324 and 380 within the aryl hydrocarbon receptor 1 ligand binding domain (AHR1 LBD) were shown to be responsible for reduced Japanese quail (Coturnix japonica) AHR1 activity to induce a dioxin-responsive reporter gene in comparison to chicken (Gallus gallus domesticus), and ring-necked pheasant (Phasianus colchicus) AHR1 in response to different DLCs; (4) AHR1 LBD sequences of 86 avian species were studied and differences at amino acid sites 256, 257, 297, 324, 337 and 380 were identified. It was discovered that only positions 324 and 380 play a role in AHR1 activity to induce a dioxin-responsive gene; (5) in COS-7 cells expressing chicken AHR1, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 2,3,4,7,8-pentachlorodibenzofuran (PeCDF) are equipotent inducers of the reporter gene and bind with similar affinity to chicken AHR1, however, in the cells expressing pheasant, Japanese quail and common tern (Sterna hirundo) AHR1, PeCDF is a stronger inducer than TCDD. PeCDF also binds with higher affinity to pheasant and quail AHR1 than TCDD. The results of this thesis show that embryo lethal effect of DLCs in avian species can be predicted by use of two new non-lethal methods: (1) the LRG assay and (2) determination of the identity of the amino acids at positions 324 and 380. The findings and methods described in this thesis will be of use for environmental risk assessments of DLCs.

No description available.

The aryl hydrocarbon receptor (AhR) carboxyl terminal transcriptional activation domain was cloned, purified in denatured conditions from bacteria, refolded via limited dialysis, and analyzed for proper refolding via co-immunoprecipitation with the known binding partner SRC-1. This AhR NΔ515 transactivation domain construct was used, along with amino terminal AhR deletion constructs AhR CΔ274 and AhR CΔ553, to attempt to elucidate the nature of the interaction between AhR and p23 in vitro.

No description available.

No description available.

Le bisphénol A (BPA) est un perturbateur endocrinien couramment employé dans l’industrie agroalimentaire, en particulier pour les matériaux en contact des denrées alimentaires. Son utilisation dans la fabrication de polycarbonates et de résines époxy, recouvrant la face interne des boîtes de conserve et des canettes, en fait un contaminant ubiquitaire de l’alimentation humaine. L’augmentation de l’exposition humaine à ce contaminant a été corrélée avec la récurrence de certains troubles comme l’intolérance alimentaire, l’obésité ou le diabète de type 2. Ces dernières années, une attention particulière a été portée sur sa capacité à perturber différentes fonctions physiologiques, dont celle du système immunitaire, après exposition périnatale à des niveaux environnementaux pertinents pour l’Homme. Dans une première étude, nous avons montré qu’une exposition périnatale au BPA à 50 µg/kg de poids corporel/jour induit une diminution de l’activité anti-microbienne corrélée à une chute de l’expression du lysozyme dans l’iléon de la descendance femelle. La perméabilité intestinale de ces individus augmente en association avec le niveau d’IFN- dans les muqueuses du côlon. De plus, nous observons une diminution des plasmocytes à IgA associée à une perte de sécrétion d’IgA dans les fèces, démontrant un défaut de la fonction barrière et des défenses de l’intestin chez la descendance BPA. De manière intéressante, une diminution de la fréquence des ILC3 intestinaux est observée chez ces individus, avec une augmentation du niveau d’IgG sanguin dirigé contre une E.coli commensale. Ces effets sont associés à un défaut de maturation et de capacité migratoire des cellules de la lamina propria (LP) et de la rate. L’exposition périnatale au BPA provoque une augmentation de la sécrétion d’IFN- et d’IL-17 après re-stimulation in vitro CD3/CD28 des cellules de la LP, et une réponse de type Th17 dans la rate. Réunis, ces effets confortent la capacité du BPA, lors d’une exposition périnatale, à induire une intolérance alimentaire chez la descendance femelle. Dans une seconde étude, nous avons mis en évidence que l’exposition périnatale au BPA, à la même dose, induit des perturbations de l’homéostasie du système immunitaire intestinal et systémique chez la descendance mâle au jour 45, via une diminution de la fréquence des Th1 et Th17 dans la LP et une augmentation de la réponse Th1 et Th17 dans la rate. Ces impacts apparaissent en parallèle avec une altération de la sensibilité au glucose, une diminution de la sécrétion d’IgA dans les fèces et un appauvrissement des bifodobacteria dans le microbiote intestinal de ces individus. L’ensemble de ces évènements précède l’infiltration de macrophages M1 pro-inflammatoires dans le tissu adipeux péri-gonadique, en association avec une diminution de la sensibilité à l’insuline et une augmentation du poids corporel apparaissant avec le vieillissement (jour 170) chez la descendance BPA. Cette étude longitudinale a permis de proposer une séquence d’évènements aboutissant à un phénotype obèse et au T2D lors d’une exposition périnatale au BPA, et ainsi de comprendre le rôle du système immunitaire en lien avec le microbiote intestinal dans le développement de ces désordres métaboliques. Enfin, nous émettons l’hypothèse que les bisphénols S et F, deux analogues structuraux du BPA, peuvent disposer de capacités immunomodulatrices équivalentes à celles du BPA, susceptibles de provoquer les mêmes troubles chez la descendance. Nous avons testé cette hypothèse de manière préliminaire chez la descendance femelle après exposition périnatale au BPS et au BPF. Des résultats préliminaires d’études in vitro sur ces deux composés en comparaison au BPA sont également apportés. Ce travail de thèse contribue à accroître les connaissances relatives aux effets immunotoxiques des bisphénols dans le contexte de l’origine développementale des pathologies chroniques de l’adulte (DOHaD). / The endocrine disruptor bisphenol A (BPA) is commonly found in food industry, more precisely in food contact packaging. BPA is used to manufacture polycarbonate plastics and epoxy resins lining food and beverage cans, becoming an ubiquitous contaminant in human food. The extent of human exposure to this chemical is thought to be correlated with the occurrence of disorders like food intolerance, obesity and type-2 diabetes (T2D). During last years, a particular interest have been raised about its ability to disrupt various physiological functions, including immune system, after perinatal exposure at relevant environmental doses for Human. In the first study, we showed that perinatal exposure to BPA (50 µg/kg body weight/day) decreased anti-microbial activity and ileal lysozyme expression in the female mouse offspring. In those mice, we observed an increased gut permeability, in association with an increase of colonic IFN- level. Moreover, we observed a decrease of IgA+ cells with a loss of IgA secretion into faeces, depicting intestinal barrier and defense function defects in BPA female offspring. Interestingly, a decrease of the intestinal ILC3 frequency associated with an increase of IgG against commensal E.coli in sera have been observed in these individuals. These effects were linked to a defect of maturation and migratory ability of dendritic cells from lamina propria (LP) and spleen. Perinatal exposure to BPA also increased IFN- and IL-17 secretions after in vitro stimulation in the gut and elicited Th17 response in the spleen. Altogether, these effects support the ability of a perinatal exposure to BPA to induce oral intolerance with ageing in female offspring. Secondly, we showed that perinatal exposure to BPA at the same dose led to intestinal and systemic immune system homeostasis disturbances in male mouse offspring at day 45, through a decrease of Th1 and Th17 frequencies in the LP and an increase of Th1 and Th17 response in spleen. These effects were associated with an altered glucose sensibility, a decrease of faecal IgA secretion and a fall of bifidobacteria in the microbiota of these individuals. These BPA-mediated events precede infiltration of pro-inflammatory M1 macrophages in gonadal white adipose tissue, together with a decreased insulin sensitivity and an increased weight gain. This longitudinal study allowed us to better understand the sequential events linked to perinatal exposure to BPA that lead to obesity and T2D, and highlighted the role of immune system linked to gut microbiota in the development of these metabolic disorders. Finally, we hypothesized that two structural analogs of BPA –i.e., Bisphenol S and F- can display similar immune-modulatory effects that could lead to similar developmental disturbances than BPA in exposed-offspring. This hypothesis was tested in a preliminary experiment in female mouse offspring perinatally exposed to BPS and BPF. We also provided preliminary results of these two compounds, compared to BPA, from an in vitro study. This thesis contributes to the increase knowledge about the immunotoxic effects of bisphenol compounds in the context of the Developmental Origins of Health and Disease (DOHaD).

Effects of man made pollutants on an ecosystem are initiated at the cellular level where a prime determinant for survival of an organism is its ability to metabolise and excrete toxic chemicals or their metabolites, thereby preventing cellular toxicity or damage to germ cell DNA. Cytochrome P450 (CYP) enzymes are responsible (in concert with the remainder of the Ah battery enzymes) for the metabolism of numerous xenobiotics and endogenous compounds, including the metabolic activation of most environmental toxic chemicals and carcinogens. Genetic polymorphisms which affect performance of these enzymatic detoxification systems may alter tolerance to pollutants and thus survival in polluted environments. Alterations in the susceptibility of individuals and the development of resistant populations has arisen by forced selection of populations with variant genes, resulting in increased detoxification capacity. There is evidence for such scenarios of variations in activities of pollutant biotransforming enzymes of fish contributing to survival in polluted estuarine environments and several chemically resistant populations have been identified in the USA and Europe. In fish it has been demonstrated that CYP1A enzyme activity is required to activate some carcinogenic xenobiotics to a metabolic state in which they can form DNA adducts. The mechanism of reduced CYP1A expression in highly contaminated populations may therefore represent resistance to chemical stressors. European flounder (Platichthys flesus) from some waterways which have a long history of severe sedimentary contamination do not show elevated levels of CYP1A. The aim of the current study was to investigate whether any heritable differences were apparent between offspring from parents inhabiting long-term polluted and pristine areas. Flounder were obtained from a highly polluted estuary in the UK and crossed with fish from a relatively pristine environment. Offspring were raised in communal tanks in order to standardise environmental conditions, and allow investigations into the genetic variation of CYP1A. To allow identification of offspring to parental fish, polymorphic microsatellite loci were isolated and characterised for the flounder. Novel cDNA probes to transcription factors in the detoxification pathway (AhR2 and ARNT2) were cloned for flounder, and RT-PCR / Southern blot methods were developed for quantitation of gene transcript levels. A novel method of CYP1A quantification using real-time PCR was developed. PAH and PCB exposure trials were carried out on mixed batch offspring, and CYP1A gene transcript levels assessed using Northern blot and real-time PCR techniques. Offspring were genotyped to their parents using the microsatellites obtained, and CYP1A transcript levels were correlated with clean and polluted areas. CYP1A was further correlated to transcription factor expression, and data are presented. Following exposure to the commercial PCB mixture, Aroclor 1254, CYP1A transcript levels were found to be significantly lower in families whose parents originated from a polluted area. This observation indicates that there is a possible genetic component to variation in CYP1A levels, and that these fish may have acquired a heritable tolerance to polluted areas. The lack of induction, or correlation with CYP1A levels, of AhR2 and ARNT2 expression indicates a possible AhR independent pathway for the metabolism of PCBs in the flounder. © Tom Dixon 2003 http://www.tomdixon.org

No description available.

No description available.

<p>Subteratogenic and other low-level chronic exposures to toxicant mixtures are an understudied threat to environmental and human health. It is especially important to understand the effects of these exposures for contaminants, such as polycyclic aromatic hydrocarbons (PAHs) a large group of more than 100 individual compounds, which are important environmental (including aquatic) contaminants. Aquatic sediments constitute a major sink for hydrophobic pollutants, and studies show PAHs can persist in sediments over time. Furthermore, estuarine systems (namely breeding grounds) are of particular concern, as they are highly impacted by a wide variety of pollutants, and estuarine fishes are often exposed to some of the highest levels of contaminants of any vertebrate taxon. Acute embryonic exposure to PAHs results in cardiac teratogenesis in fish, and early life exposure to certain individual PAHs and PAH mixtures cause heart alterations with decreased swimming capacity in adult fish. Consequently, the heart and cardiorespiratory system are thought to be targets of PAH mixture exposure. While many studies have investigated acute, teratogenic PAH exposures, few studies have longitudinally examined the impacts of subtle, subteratogenic PAH mixture exposures, which are arguably more broadly applicable to environmental contamination scenarios. The goal of this dissertation was to highlight the later-life consequences of early-life exposure to subteratogenic concentrations of a complex, environmentally relevant PAH mixture.</p><p>A unique population of Fundulus heteroclitus (the Atlantic killifish or mummichog, hereafter referred to as killifish), has adapted to creosote-based polycyclic aromatic hydrocarbons (PAHs) found at the Atlantic Wood Industries (AW) Superfund site in the southern branch of the Elizabeth River, VA, USA. This killifish population survives in a site heavily contaminated with a mixture of PAHs from former creosote operations. They have developed resistance to the acute toxicity and teratogenic effects caused by the mixture of PAHs in sediment from the site. The primary goal of this dissertation was to compare and contrast later-life outcomes of early-life, subteratogenic PAH mixture exposure in both the Atlantic Wood killifish (AW) and a naïve reference population of killifish from King’s Creek (KC; a relatively uncontaminated tributary of the Severn River, VA). Killifish from both populations were exposed to subteratogenic concentrations of a complex PAH-sediment extract, Elizabeth River Sediment Extract (ERSE), made by collecting sediment from the AW site. Fish were reared over a 5-month period in the laboratory, during which they were examined for a variety of molecular, physiological and behavioral responses. </p><p>The central aims of my dissertation were to determine alterations to embryonic gene expression, larval swimming activity, adult behavior, heart structure, enzyme activity, and swimming/cardiorespiratory performance following subteratogenic exposure to ERSE. I hypothesized that subteratogenic exposure to ERSE would impair cardiac ontogenic processes in a way that would be detectable via gene expression in embryos, and that the misregulation of cardiac genes would help to explain activity changes, behavioral deficits, and later-life swimming deficiencies. I also hypothesized that fish heart structure would be altered. In addition, I hypothesized that the AW killifish population would be resistant to developmental exposures and perform normally in later life challenges. To investigate these hypotheses, a series of experiments were carried out in PAH-adapted killifish from Elizabeth River and in reference killifish. As an ancillary project to the primary aims of the dissertation, I examined the toxicity of weaker aryl hydrocarbon receptor (AHR) agonists in combination with fluoranthene (FL), an inhibitor of cytochrome P4501A1 (CYP1A1). This side project was conducted in both Danio rerio (zebrafish) and the KC and AW killifish.</p><p>Embryonic gene expression was measured in both killifish populations over an ERSE dose response with multiple time points (12, 24, 48, and 144 hours post exposure). Genes known to play critical roles in cardiac structure/development, cardiac function, and angiogenesis were elevated, indicating cardiac damage and activation of cardiovascular repair mechanisms. These data helped to inform later-life swimming performance and cardiac histology studies. Behavior was assessed during light and dark cycles in larvae of both populations following developmental exposure to ERSE. While KC killifish showed activity differences following exposure, AW killifish showed no significant changes even at concentrations that would cause overt cardiac toxicity in KC killifish. Juvenile behavior experiments demonstrated hyperactivity following ERSE exposure in KC killifish, but no significant behavioral changes in AW killifish. Adult swimming performance via prolonged critical swimming capacity (Ucrit) demonstrated performance costs in the AW killifish. Furthermore, swimming performance decline was observed in KC killifish following exposure to increasing dilutions of ERSE. Lastly, cardiac histology suggested that early-life exposure to ERSE could result in cardiac structural alteration and extravasation of blood into the pericardial cavity.</p><p>Responses to AHR agonists resulted in a ranking of relative potency for agonists, and determined which agonists, when combined with FL, caused cardiac teratogenesis. These experiments showed interesting species differences for zebrafish and killifish. To probe mechanisms responsible for cardiotoxicity, a CYP1A-morpholino and a AHR2-morpholino were used to mimic FL effects or attempt to rescue cardiac deformities respectively. Findings suggested that the cardiac toxicity elicited by weak agonist + FL exposure was likely driven by AHR-independent mechanisms. These studies stand in contrast to previous research from our lab showing that moderate AHR agonist + FL caused cardiac toxicity that can be partially rescued by AHR-morpholino knockdown.</p><p>My findings will form better characterization of mechanisms of PAH toxicity, and advance our understanding of how subteratogenic mixtures of PAHs exert their toxic action in naïve killifish. Furthermore, these studies will provide a framework for investigating how subteratogenic exposures to PAH mixtures can impact aquatic organismal health and performance. Most importantly, these experiments have the potential to help inform risk assessment in fish, mammals, and potentially humans. Ultimately, this research will help protect populations exposed to subtle PAH-contamination.</p> / Dissertation